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3.
VMWARE WHITE PAPER
Virtualization Overview
Introduction
Virtualization in a Nutshell
Among the leading business challenges confronting CIOs and
IT managers today are: cost-effective utilization of IT infrastructure; responsiveness in supporting new business initiatives;
and flexibility in adapting to organizational changes. Driving
an additional sense of urgency is the continued climate of IT
budget constraints and more stringent regulatory requirements.
Virtualization is a fundamental technological innovation that
allows skilled IT managers to deploy creative solutions to such
business challenges.
Simply put, virtualization is an idea whose time has come.
The term virtualization broadly describes the separation of a
resource or request for a service from the underlying physical
delivery of that service. With virtual memory, for example,
computer software gains access to more memory than is
physically installed, via the background swapping of data to
disk storage. Similarly, virtualization techniques can be applied
to other IT infrastructure layers - including networks, storage,
laptop or server hardware, operating systems and applications.
This blend of virtualization technologies - or virtual infrastructure - provides a layer of abstraction between computing,
storage and networking hardware, and the applications running
on it (see Figure 1). The deployment of virtual infrastructure
is non-disruptive, since the user experiences are largely
unchanged. However, virtual infrastructure gives administrators
the advantage of managing pooled resources across the enterprise, allowing IT managers to be more responsive to dynamic
organizational needs and to better leverage infrastructure
investments.
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Before Virtualization:
• Single OS image per machine
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After Virtualization:
• Software and hardware tightly coupled
• Hardware-independence of operating
system and applications
• Running multiple applications on same machine
often creates conflict
• Virtual machines can be provisioned to any
system
• Underutilized resources
• Can manage OS and application as a single
unit by encapsulating them into virtual
machines
• Inflexible and costly infrastructure
Figure 1: Virtualization
3

4.
VMWARE WHITE PAPER
Virtualization Approaches
Using virtual infrastructure solutions such as those from
VMware, enterprise IT managers can address challenges that
include:
While virtualization has been a part of the IT landscape for
decades, it is only recently (in 1998) that VMware delivered
the benefits of virtualization to industry-standard x86-based
platforms, which now form the majority of desktop, laptop and
server shipments. A key benefit of virtualization is the ability to
run multiple operating systems on a single physical system and
share the underlying hardware resources – known as partitioning.
• Server Consolidation and Containment – Eliminating ‘server
sprawl’ via deployment of systems as virtual machines (VMs)
that can run safely and move transparently across shared
hardware, and increase server utilization rates from 5-15%
to 60-80%.
• Test and Development Optimization – Rapidly provisioning
test and development servers by reusing pre-configured
systems, enhancing developer collaboration and standardizing development environments.
Today, virtualization can apply to a range of system layers,
including hardware-level virtualization, operating systemlevel virtualization, and high-level language virtual machines.
Hardware-level virtualization was pioneered on IBM mainframes
in the 1970s, and then more recently Unix/RISC system vendors
began with hardware-based partitioning capabilities before
moving on to software-based partitioning.
• Business Continuity – Reducing the cost and complexity of
business continuity (high availability and disaster recovery
solutions) by encapsulating entire systems into single files
that can be replicated and restored on any target server,
thus minimizing downtime.
For Unix/RISC and industry-standard x86 systems, the two
approaches typically used with software-based partitioning are
hosted and hypervisor architectures (See Figure 2). A hosted
approach provides partitioning services on top of a standard
operating system and supports the broadest range of hardware
configurations. In contrast, a hypervisor architecture is the first
layer of software installed on a clean x86-based system (hence
it is often referred to as a “bare metal” approach). Since it has
direct access to the hardware resources, a hypervisor is more
efficient than hosted architectures, enabling greater scalability,
robustness and performance.
• Enterprise Desktop – Securing unmanaged PCs, workstations and laptops without compromising end user
autonomy by layering a security policy in software around
desktop virtual machines.
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Hosted Architecture
Bare-Metal (Hypervisor) Architecture
• Installs and runs as an application
• Lean virtualization-centric kernel
• Relies on host OS for device support
and physical resource management
• Service Console for agents and helper
applications
Figure 2: Virtualization Architectures
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5.
VMWARE WHITE PAPER
Hypervisors can be designed to be tightly coupled with operating systems or can be agnostic to operating systems. The latter
approach provides customers with the capability to implement
an OS-neutral management paradigm, thereby providing
further rationalization of the data center.
Application-level partitioning is another approach, whereby
many applications share a single operating system, but this
offers less isolation (and higher risk) than hardware or software
partitioning, and limited support for legacy applications or
heterogeneous environments. However, various partitioning
techniques can be combined, albeit with increased complexity.
Hence, virtualization is a broad IT initiative, of which partitioning
is just one facet. Other benefits include the isolation of virtual
machines and the hardware-independence that results from
the virtualization process. Virtual machines are highly portable,
and can be moved or copied to any industry-standard (x86based) hardware platform, regardless of the make or model.
Thus, virtualization facilitates adaptive IT resource management,
and greater responsiveness to changing business conditions
(see Figures 3-5).
To provide advantages beyond partitioning, several system
resources must be virtualized and managed, including CPUs,
main memory, and I/O, in addition to having an inter-partition
resource management capability. While partitioning is a useful
capability for IT organizations, true virtual infrastructure delivers
business value well beyond that.
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Figure 3: Traditional Infrastructure
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8.
VMWARE WHITE PAPER
How Virtualization Complements NewGeneration Hardware
Extensive ‘scale-out’ and multi-tier application architectures are
becoming increasingly common, and the adoption of smaller
form-factor blade servers is growing dramatically. Since the
transition to blade architectures is generally driven by a desire
for physical consolidation of IT resources, virtualization is an
ideal complement for blade servers, delivering benefits such as
resource optimization, operational efficiency and rapid provisioning.
The latest generation of x86-based systems feature processors
with 64-bit extensions supporting very large memory capacities. This enhances their ability to host large, memory-intensive
applications, as well as allowing many more virtual machines to
be hosted by a physical server deployed within a virtual infrastructure. The continual decrease in memory costs will further
accelerate this trend.
Likewise, the forthcoming dual-core processor technology
significantly benefits IT organizations by dramatically lowering
the costs of increased performance. Compared to traditional
single-core systems, systems utilizing dual-core processors will
be less expensive, since only half the number of sockets will be
required for the same number of CPUs. By significantly lowering
the cost of multi-processor systems, dual-core technology will
accelerate data center consolidation and virtual infrastructure
projects,
Beyond these enhancements, VMware is also working closely
with both Intel and AMD to ensure that new processor technology features are exploited by virtual infrastructure to the fullest
extent. In particular, the new virtualization hardware assist
enhancements (Intel’s “VT” and AMD’s “Pacifica”) will enable
robust virtualization of the CPU functionality. Such hardware
virtualization support does not replace virtual infrastructure, but
allows it to run more efficiently.
Para-virtualization
Although virtualization is rapidly becoming mainstream technology, the concept has attracted a huge amount of interest,
and enhancements continue to be investigated. One of these is
para-virtualization, whereby operating system compatibility is
traded off against performance for certain CPU-bound applications running on systems without virtualization hardware assist
(see Figure 7). The para-virtualized model offers potential performance benefits when a guest operating system or application
is ‘aware’ that it is running within a virtualized environment,
and has been modified to exploit this. One potential downside
of this approach is that such modified guests cannot ever be
migrated back to run on physical hardware.
In addition to requiring modified guest operating systems, paravirtualization leverages a hypervisor for the underlying technology. In the case of Linux distributions, this approach requires
extensive changes to an operating system kernel so that it can
coexist with the hypervisor. Accordingly, mainstream Linux
distributions (such as Red Hat or SUSE) cannot be run in a paravirtualized mode without some level of modification. Likewise,
Microsoft has suggested that a future version of the Windows
operating system will be developed that can coexist with a new
hypervisor offering from Microsoft.
Yet para-virtualization is not an entirely new concept. For
example, VMware has employed it by making available as
an option enhanced device drivers (packaged as VMware
Tools) that increase the efficiency of guest operating systems.
Furthermore, if and when para-virtualization optimizations are
eventually built into commercial enterprise Linux distributions,
VMware’s hypervisor will support those, as it does all mainstream operating systems.
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Figure 7: Para-virtualization
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9.
VMWARE WHITE PAPER
VMware’s Virtualization Portfolio
VMware is the only provider of high-performance virtualization
products that give customers a real choice in operating systems.
VMware supports: Windows 95/98/NT/2K/2003/XP/3.1/MS-DOS
6; Linux (Red Hat, SUSE, Mandrake, Caldera); FreeBSD (3.x, 4.04.9); Novell (NetWare 4,5,6); Sun Solaris 9 and 10 (experimental).
VMware pioneered x86-based virtualization in 1998 and
continues to be the innovator in that market, providing the
fundamental virtualization technology for all leading x86based hardware suppliers. The company offers a variety of
software-based partitioning approaches, utilizing both hosted
(Workstation and VMware Server) and hypervisor (ESX Server)
architectures. (see Figure 8)
VMware’s virtual machine (VM) approach creates a uniform
hardware image – implemented in software – on which operating systems and applications run. On top of this platform,
VMware’s VirtualCenter provides management and provisioning
of virtual machines, continuous workload consolidation across
physical servers and VMotion™ technology for virtual machine
mobility.
VirtualCenter is virtual infrastructure management software that
centrally manages an enterprise’s virtual machines as a single,
logical pool of resources. With VirtualCenter, an administrator can manage thousands of Windows NT, Windows 2000,
Windows 2003, Linux and NetWare servers from a single point
of control.
VMware is designed from the ground up to ensure compatibility with customers’ existing software infrastructure investments.
This includes not just operating systems, but also software for
management, high availability, clustering, replication, multipathing, and so on.
VMware’s hypervisor-based products and solutions have been
running at customer sites since 2001, with more than 75% of
customers running ESX Server in production deployments. As
the clear x86 virtualization market leader, VMware is uniquely
positioned to continue providing robust, supportable, highperformance virtual infrastructure for real-world, enterprise data
center applications.
Unique to VMware is the VMotion technology, whereby live,
running virtual machines can be moved from one physical
system to another while maintaining continuous service availability. VMotion thus allows fast reconfiguration and optimization of resources across the virtual infrastructure.
App
App
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App
App
OS
OS
OS
OS
CONSISTENT VIRTUAL HARDWARE PLATFORM
Open Interfaces
VMware
Infrastructure
ACE
System Architecture
& Highlights
Workstation
VMware Server
ESX Server
Secured Enterprise
Desktop
Technical
Desktop
Departmental
Computing
Enterprise
Computing
Hosted on Windows
Hosted on Windows
or Linux
Hosted on Windows
or Linux
Bare Metal
V-SMP Option
Mgmt Server,
Console & APIs
VMotion
Figure 8: Single Virtual Platform Desktop to Enterprise
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10.
VMWARE WHITE PAPER
Glossary
Virtual Machine
A representation of a real machine using software that provides
an operating environment which can run or host a guest operating system.
Guest Operating System
An operating system running in a virtual machine environment
that would otherwise run directly on a separate physical system.
Virtual Machine Monitor
Software that runs in a layer between a hypervisor or host operating system and one or more virtual machines that provides
the virtual machine abstraction to the guest operating systems.
With full virtualization, the virtual machine monitor exports a
virtual machine abstraction identical to a physical machine, so
that standard operating systems (e.g., Windows 2000, Windows
Server 2003, Linux, etc.) can run just as they would on physical
hardware.
Hypervisor
A thin layer of software that generally provides virtual partitioning capabilities which runs directly on hardware, but underneath higher-level virtualization services. Sometimes referred to
as a “bare metal” approach.
Hosted Virtualization
A virtualization approach where partitioning and virtualization
services run on top of a standard operating system (the host).
In this approach, the virtualization software relies on the host
operating system to provide the services to talk directly to the
underlying hardware.
Para-virtualization
A virtualization approach that exports a modified hardware
abstraction which requires operating systems to be explicitly
modified and ported to run.
Virtualization Hardware Support
Industry standard servers will provide improved hardware
support for virtualization. Initial hardware support includes
processor extensions to address CPU and some memory
virtualization. Future support will include I/O virtualization, and
eventually more complex memory virtualization management.
Hardware-level virtualization
Here the virtualization layer sits right on top of the hardware
exporting the virtual machine abstraction. Because the virtual
machine looks like the hardware, all the software written for it
will run in the virtual machine.
10
Operating system–level virtualization
In this case the virtualization layer sits between the operating
system and the application programs that run on the operating
system. The virtual machine runs applications, or sets of applications, that are written for the particular operating system being
virtualized.
High-level language virtual machines
In high-level language virtual machines, the virtualization layer
sits as an application program on top of an operating system.
The layer exports an abstraction of the virtual machine that can
run programs written and compiled to the particular abstract
machine definition. Any program written in the high-level
language and compiled for this virtual machine will run in it.
For more information:
http://www.vmware.com
http://www.vmware.com/solutions/
http://www.vmware.com/vinfrastructure/